Magnetic latches have been known heretofore. For example, Pang U.S. Pat. No. 4,000,481, dated Dec. 28, 1976, shows an electrically releasable permanent magnet latch. The armature must be set into its latch position by external means and is then held there by a pair of permanent magnets. Energization of the coil creates a magnetic flux which opposes the permanent magnet flux to permit the operating spring to overcome the armature holding force thereby to allow the spring to operate the armature.
Using magnetic cores that saturate at different current levels of a common winding so as to keep a switch open at high currents and to allow the switch to close at low currents has also been known heretofore. For example, E. R. Stoekle U.S. Pat. No. 1,525,697, dated Feb. 10, 1925, discloses an electromagnet that is especially applicable for use as a lockout switch. This electromagnet has two magnetic circuits such that for currents above a certain predetermined value in the common winding, one core is relatively saturated while the other core is relatively unsaturated so that the pull exerted on the armature by the flux in the unsaturated restraining magnetic circuit exceeds that exerted by the flux in the saturated closing magnetic circuit to keep the contacts open. As the current through the magnetic winding decreases, the flux in both magnetic circuits decreases. However, the flux in the restraining magnetic circuit decreases very much more rapidly than the flux in the closing magnetic circuit. When the current through the magnet winding falls below a predetermined value, the flux in the restraining magnetic circuit has decreased so much that the pull exerted thereby is overcome by the pull exerted by the flux in the closing magnetic circuit and the switch closes.
While these prior devices have been useful for their intended purposes, it has been found desirable to provide an improved snap-acting magnetic latch that is small in size and efficient in operation and is especially applicable to lightweight products.